1. Field of the Invention
The present invention relates to a method for producing wall covering with relief, such as for example wallpaper, comprising:                step a providing a base;        step b applying a heat-expandable material to this base in a continuous process using an analogue printing technique;        step c applying one or more liquids, which influence the expansion of the expandable material, in a desired pattern, in a continuous process onto the base onto which the expandable material has been applied;        step d heating the base with the expandable material which has been applied thereto and the one or more liquids applied thereto to a temperature at which the expandable material expands.        
In this context, the expression wall covering with relief is understood to mean that the surface of this wall covering comprises at least two heights or thicknesses which differ from those which the base originally comprised. In this case, such a relief may cover the entire surface of the base or only part thereof.
Such a wall covering may, for example, be wallpaper or, for example, a reproduction of a painting, etc.
It is possible to use a plurality of bases to obtain such a wall covering, such as for example bases in paper, fabrics, non-woven, plastic, cardboard, etc. These bases may optionally be provided with one or more finishing layers before the relief is applied and may also be provided with one or more finishing layers after the relief has been applied. These finishing layers may, for example, comprise colour and relief.
The expandable materials which can be used for this purpose are also generally used and well-known in the wallpaper and wall covering industry.
This may, for example, comprise a so-called PVC paste, containing, for example:                polyvinyl chloride (PVC) and/or variants, such as for example polyvinylidene chloride, polyvinyl acetate, polyacrylate, polymethacrylate, etc.supplemented by one or more:        softeners, such as for example phthalates, or environmentally friendly alternatives, etc.        and/or fillers, such as for example calcium, etc.        and/or diluents;        and/or stabilizers,        and/or blowing agents, such as for example azodicarbonamide, azoisobutyronitrile, benzene, sulfohydrazide, sodium bicarbonate, etc.        and/or catalysts;        and/or accelerators.        
2. Related Art
The liquids which influence the expansion of the expandable material may be liquids which promote expansion of this expandable material and/or liquids which hinder or prevent expansion of the expandable material, such as are known in the wallpaper and wall covering industry, inter alia for example as described in U.S. Pat. No. 5,712,018 A.
The known techniques by means of which such a wall covering with relief is formed in a continuous process are usually relatively expensive when limited print runs are being produced. In applications, such as for example with wallpaper, where relief is applied in a continuous process using rotating cylinders, the known methods have the additional drawback that the pattern which is applied to the base in relief, is limited due to the repeat which is inherent to the continuous process.
With wallpaper, it is for example possible to create a relief by applying a material on a support or base. When a certain shape or design is adhered to during the application of this material, the resulting relief will assume this shape or design or adhere thereto. In addition, it is possible to vary the height of the pattern by applying different amounts of material to the base at different locations or by applying materials of different composition and with different expansion properties alternately using different cylinders in a continuous process. In this way, it is possible to apply a decoration which uses three dimensions (length, width and height).
Using current continuous production methods for applying relief to wallpaper, this relief is applied by means of mechanical embossing, chemical embossing or screen printing techniques.
In the case of mechanical embossing, a layer of (optionally coloured) PVC paste is first applied to a base as expandable material, after which it is heated in order to cause the PVC paste to expand in the subsequent step in the production process. Then, the desired relief is embossed onto this layer of PVC paste using one cylinder or a combination of two cylinders on which the desired relief has been applied in positive and/or negative. If it is desired to produce coloured wallpaper, the base has to be printed with additional colouring inks before or after embossing.
In the case of chemical embossing, a layer of (optionally coloured) PVC paste is first applied to a base as expandable material. At a later stage of the production process, this is then printed with liquids which influence the expansion of the expandable material using analogue printing techniques in a continuous process. This may be liquids which promote expansion of this expandable material and/or liquids which hinder or prevent expansion of the expandable material. Subsequently, the PVC paste is heated, as a result of which it expands. At the locations where this paste has been printed with liquids which promote and/or hinder or prevent the expansion, this paste will expand to a greater or lesser degree, respectively, than in the locations where this paste is not printed. Wallpaper which has been produced in such a manner is also known as scope wallpaper.
In the case of screen-printing techniques, a relief-defining liquid (usually expandable PVC paste) is applied to a base by means of a cylinder in which openings have been made according to the desired relief pattern. Subsequently, the base is heated in an oven in order to cause the PVC paste to expand, resulting in the desired relief. If it is desired to produce coloured wallpaper, different printing cylinders may be used in which case a different colour of PVC paste is applied to the base by each cylinder. With the current installations, the number of colours which can be applied is thus usually limited to a maximum of 12 colours. If more (variations in) colours are desired, it is possible, if desired, to print this wallpaper with coloured inks beforehand or in a subsequent step.
With mechanical embossing and chemical embossing as well as with screen-printing techniques in a continuous process, the intended pattern which is applied in relief is limited by the repeat of said cylinders by means of which the relief is either impressed or applied using PVC paste. If it is desired to apply an additional pattern to the support, a second printing cylinder has to be used or a second identical treatment with another printing cylinder has to be repeated.
All these techniques typically are also accompanied by a loss of material during the starting up of a machine in which, inter alia, the different cylinders have to be brought in line with one another so that they run synchronously.